The situation with computer languages is somewhat like that with human languages:

• Translator: takes a complete document in one language and translates it into a complete document in a second language, which can then be used by a reader of the second language.
• Interpreter: acts as an intermediate between a speaker of one language and a speaker of another language. Usually an interpreter works one sentence at a time. Immediately after a sentence is spoken in the first language, the translator converts it into the second language. You and your French translator (say) could in combination be regarded as a "virtual French speaker".

Using a human interpreter as an intermediate is slower than conversing directly in a particular language. The same is true with computer language interpreters. The interpreter has to do quite a bit of work to deal with the language it is interpreting. The extra work makes it look like the virtual processor is much slower than the real one.